Wireless communication networks have evolved complex protocols to establish and maintain reliable connections between mobile user equipment (UE) and the network. Generally, the communications between UEs and the network comprise two types: signaling (also known as control plane communications), which are “overhead” communications used to control connectivity, transmission power, and technical features (e.g., modulation and coding); and IP data (also known as user plane communications), which comprise the content being communicated (e.g., digital voice, text, images, video, and the like). Both signaling and IP data transfer occur across the air interface, which has limited bandwidth.
Signaling congestion is a recurring difficulty in wireless communication networks. It is well known in large arena venues, but also occurs almost anywhere where large masses of people commute or gather. The scheduler weight of signaling is typically much higher than for IP data. The reasons for that are many, some are rational and based on concerns to not risk overloading some bottleneck resource; some are based on more traditional concerns and obligations to provide secure and overly reliable mechanisms for connection control and telecom lines.
When signaling congestion occurs, the capacity for IP data is drastically decreased, regardless of its initial size. The scheduling delay of IP data increases without limit, and very rapidly the system throughput of IP data can be severely if not completely throttled. The signaling congestion itself increases rapidly from an exponential increase of various types of high priority signaling aiming to maintain or re-establish connectivity over the congested air interface, all of which further represses IP data. Packets are delayed and also largely fragmented on the Layer 2 level in the course of these events. There are discouraging observations from radio based mobile communication networks where as little as a 10-byte chunk of a 1500-byte packet is consecutively scheduled every 50th up to 150th ms, while at the same time there is a delay budget of 300 ms for the packet itself. However, from the viewpoint of the radio-based scheduler and data transport layers, nothing appears abnormal. In fact, it is one of the main features of data transport and adaption layers, such as the Layer 2 Radio Link Protocol (RLC) and Medium Access Protocol (MAC) of 3GPP LTE, to fragment and adapt incoming IP data to whatever sizes and formats can be sustained over a congested radio channel (RLC is specified in 3GPP TS 36.322; MAC in 3GPP TS 36.321).
Many current methods attempting to address signaling congestion focus on preempting low priority IP bearers, and UEs with such bearers, and ultimately removing associated services from the system. However, preemption only serves to perpetuate the problem, since devices will try to re-establish, and will continue to request service and data transmission resources. The network interactions are built on standards such as MAC, RLC, RRC, and TCP, which use persistent retransmission and re-establishment methods, all of which will further increase the signaling. Accordingly, preemption effectively transforms users that are known to use low-priority IP bearers into users with high-priority signaling.
Among the more drastic methods to handle signaling congestion are those that stop admitting users of low-priority IP bearers, or bar users from attempting to access if they only have delay-tolerant data. There are numerous deficiencies to such a strategy. The latency in idle mode is large; it takes time to set up a new control plane whenever user data appears which is not delay-tolerant. There is also an inherent inconsistency with a strategy that aims to combat signaling congestion, which must continuously reestablish control planes and rely on signaling to achieve that. A better approach would be to maintain the connection, but use methods that relax the pressure on resources used for signaling.
UEs may schedule uplink (UL) transmissions in two ways. A UE that is UL synchronized may send a scheduling request on the Physical Uplink Control Channel (PUCCH), and receive from the network a grant to use the Uplink Shared Channel (UL-SCH) for dedicated data transmission. The PUCCH resources improve UL and DL throughput and reduce latency, but are available only in limited amounts. For highly loaded systems, it is beneficial to only have a subset of the RRC Connected UEs in the cell be UL synchronized—ideally, those with data transfers or requests that are not delay-tolerant.
Alternatively, a UE with delay-tolerant data or requests may allow its UL synchronization to lapse, and gather, or coalesce, its transmissions. When the UE is ready to perform a significant amount of data transfer, it may regain UL synchronization by use of the Random Access Channel (RACH). While this process takes longer for the UE to reestablish connectivity, if it has only delay-tolerant traffic there is no deleterious effect to the user, and the network is relieved of signaling congestion between the UE's connection sessions.
Hence, it is advantageous for the network to keep UEs having traffic that is not delay-tolerant UL synchronized and able to access PDCCH to schedule transmissions with minimal latency. It is also advantageous for the network to more rapidly move UEs having delay-tolerant traffic out of UL synchronization to relieve the signaling load, and allow them to infrequently establish connectivity via RACH. How long a UE remains UL synchronized between data transmissions across the air interface is controlled by the Time Alignment Timer (TAT) value, which is typically a few seconds.
With the growth of internet communications generally, and the proliferation of modern “smartphones,” much traffic across the air interface is mobile internet access, much of which is both uplink-driven (e.g., a browser sending a request to a web server) and delay-tolerant. Indeed, many apps driving UL traffic operate as “background” tasks. In contrast, “foreground” apps, such as voice communications, video or audio streaming, and the like, are not delay-tolerant. Accordingly, the UE is often in the best position to determine if its traffic is delay-tolerant or not, and may utilize this knowledge to trend toward either RACH or PDCCH access, respectively, to help alleviate network signaling congestion in an intelligent manner.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.